1. Field of the Invention
The present invention relates to earthquake base isolation of buildings and other structures. More particularly, the invention relates to antifriction base isolators.
2. Description of the Prior Art
It is considered to be the ultimate in seismic isolation to place a superstructure on roller or ball bearings. In this case, almost no horizontal force will be transmitted in a superstructure. However, extreme yieldingness under wind load and inability to restore the initial position prevented such systems from practical implementation.
The invention entitled "Earthquake Shelter" (Ser. No 07/363,592, U.S. Patent Allowed) incorporates ball bearing base isolator where the ball bearing is supported on a pedestal plate having a concave upper surface; the ball bearing permits the superstructure to remain horizontally undisturbed during an earthquake and retains its initial position with respect to the footing. But this system is not intended for resistance against wind.
The invention entitled "Earthquake Stable Support" (SU-666-266) has a sphere contained between two belts with conical recesses, each side having additional recess in its center to remain the sphere in position under wind pressure. But the conical shape of the recesses makes the system auto-tuning with the earth excitation, because the growth of the ground period is accompanied by the increase in ground displacement which in its turn gives rise to the increase of the isolated system period, and the system has to perform under periresonant conditions. Besides, functioning of a support of this kind is associated with travelling the sphere horizontally regarding the supported superstructure which generates alternating eccentrically applied vertical base reactions that might result in excitation of damaging flextural stress waves.